In gas turbine engines, multi-stage axial compressors include sets of alternating fixed vanes and rotating blades that, during operation, cooperatively produce a flow of compressed air for downstream use as a component of combustion.
As a byproduct of the compression process, components in the compressor are subjected to temperatures which vary not only in location, but also temporally, as the gas turbine progresses through a variety of operating modes, including cold start, steady state, and any number of transition conditions. Over time, these temperature differences impart varying degrees of thermal growth to the compressor components, and gaps required to allow relative motion during operation are designed to avoid unnecessary component rubbing, while minimizing leakage.
Gas turbines used for power generation may encounter particularly-difficult operating conditions, since they are often stopped and restarted in response to varying demands for power production. Engine operation in these settings may require that an engine be restarted before compressor components have uniformly cooled—known as a “hot restart.” Compressors that passively accommodate hot restarts are often designed to strike a balance between either (1) using component gaps that, particularly between rotating blade tips and associated ring segments, bigger than needed during most steady-state conditions or (2) using relatively-small gaps and abradable coatings that are sacrificially worn down during component contact. Neither of these approaches is optimal; accordingly, there exists and a need in this field for an improved compressor design capable of accommodate hot restarts without unnecessarily reducing operational efficiency.